The systems proposed and currently being evaluated for the future HDTV system of the United States of America, are primarily digital and provide relatively high resolution images. Since the signals are digital and of relatively high resolution, receivers designed to process such signals will require significant amounts of state of the art hardware, including a significant amount of video memory (VRAM). Until the technology matures, which may take ten to fifteen years, this hardware will render the HDTV receivers expensive, probably so much so as to preclude purchase by middle class families of more than one receiver per home. However most middle class families are accustomed to having a plurality of receivers in their homes. Thus there is a need for a lower cost HDTV receiver in the nearer term.
The present inventor realized that it is possible to provide a lower cost receiver of HDTV signals but at the sacrifice of some image resolution. Such receivers will still have advantages over NTSC receivers in that they will not suffer the common NTSC shortcomings such as crosscolor and crossluma, and being digital will be compatible with other digital apparatus such as home computers.
A typical HDTV signal may represent images with 1050 lines and 1440 pixels per line. A typical HDTV receiver may require, for example, four VRAMS for processing decoded signal and further memory to buffer several fields of compressed data. Considering eight bit samples, the four VRAMS will require 48.38 Mbits of very fast memory. Alternatively if the HDTV signal is decoded to normal NTSC resolution of 525 lines with 910 pixels per line, only 15.29 Mbits of slower VRAM are required, or approximately one third of that required for the high resolution image. The requirement of less memory and slower memory can effect a significant cost savings in a lower resolution receiver.